1. Field of the Invention
The present invention relates to mowing apparatuses. More specifically, the present invention relates to an apparatus for mowing lawn grass.
2. Description of the Related Art
Lawn mowers are well known devices used for cutting grass and commingled weed plants in order to maintain the appearance of an outdoor area such as a residential lawn or golf course. There are many types of lawn mowers, including rotary mowers and reel mowers. Additionally, many different cutting blades or cutter heads are known for use with lawn mowers and other plant cutting devices.
The gasoline-powered rotary mower is by far the dominant grass cutting mechanism on the market today. Less commonly, rotary mowers are powered by mains- or battery-operated electric motors. In the most familiar rotary configuration, a heavy steel blade with sharpened edges at opposing distal ends is spun at high speed around a central pivot point inside a cylindrical, open-bottomed chamber that is moved across the lawn. The blade is commonly shaped to create a zone of low air pressure above the grass in order to lift the individual shafts into the plane of the spinning blade. The power mower housing functions to prevent injury to the operator and to control the direction of discharge of the clippings generated during operation.
Different rotary cutting blade configurations are used for a variety of reasons. Burnell, in U.S. Pat. No. 5,019,113, discloses a rotary lawn mower assembly having easily detachable replacement blades. Mensing, in U.S. Pat. No. 4,532,708, discloses a blade assembly with a plurality of cutting segments arranged end to end for improved cutting. Knipe, in U.S. Pat. No. 3,964,243, shows a rotary cutting blade with detachable tines used to blow grass clippings from the mower's path.
Mullet, et al, in U.S. Pat. No. 4,916,887 discloses a rotary mulching mower using a multiplicity of cutting blades within the mower housing. Each cutting blade rotates through a different plane to cut the grass clippings into mulch. Geier, in U.S. Pat. No. 5,867,973, shows a single rotary blade consisting of multiple adjustable cutting edges to accomplish the mulching function.
Irrespective of the fact that rotary power mowers are ubiquitous, they have several significant drawbacks. The primary drawback associated with the rotary power mower is that a free-spinning steel blade is a relatively inefficient grass cutting instrument. Since a shaft of grass has little mass and can be easily deflected, the mower blade must be spun at very high power levels in order to adequately perform the cutting function. It is not uncommon to find standard rotary mower engines rated at six horsepower and above. As a consequence, in a gasoline-powered rotary mower the engine is large, noisy, creates significant air pollution, and uses relatively large amounts of energy per blade of grass cut. It was estimated in 2003 by William A. Burke, Chairman of the California South Coast Air Quality Management District, that an older gas-powered lawn mower pollutes as much in one year of typical use as a new car driven more than 86,000 miles.
Electric rotary mowers generate lower levels of noise and no (local) air pollution, but suffer from the same inherent cutting inefficiencies. As a result, they tend to be heavy and expensive due to the large battery capacity needed to generate the required inertial cutting forces.
Regardless of the power source, because the blade of the rotary mower is essentially a sharpened, if not always sharp, flail, the cut edge at the top of the living shaft of grass is often torn or ragged. A ragged grass cut is undesirable, both in terms of the appearance of the lawn and for the health of the grass. In sandy or debris-strewn soil, blades spinning at high speed erode quickly and require frequent sharpening or replacement.
Another disadvantage presented by a conventional rotary mower is the inherent danger of unintended contact with the high-speed blade. The blade is a direct threat if the user comes in contact with it, and an indirect threat if it propels an object from the housing. Grievous injuries have been sustained by both experienced and inexperienced users of rotary power mowers due to both of these conditions.
Tall grass presents another problem for conventional rotary mowers. The tendency is for tall grass to be flattened as the mower housing passes over. If the grass is very long, the housing will hold it to the ground so that it is not effectively cut.
It is believed that no current rotary lawn mowing device sufficiently addresses these problems.
Another common, and historically very significant, grass cutting mechanism is the reel mower. This device is typically constructed with a set of four to ten heavy steel blades fixed in a cylindrical form and rotated about the axis of the cylinder parallel to the ground and perpendicular to the direction of travel of the mower. The blades are generally twisted in a helical form, and positioned to graze the leading edge of a horizontal bed knife suspended at the desired cutting distance above the ground. As the mower is pushed forward, the blades of grass are swept against the bed knife and sheared between the knife and the passing helical blade. In the past, such reel mowers have been powered by both gasoline and electric motors, but the most common configuration, historically and at the present, is the human-powered “push mower”.
Compared to rotary mowers, revolving blade reel mowers have a great advantage in terms of cutting efficiency. The bed knife and revolving helical blades interact to create a ‘scissors’ action that is not only energy efficient as a cutting mechanism, but which also creates a clean cut at the top of the living shaft of grass. Lawns that are routinely cut with reel mowers, such as is commonly the practice at many golf courses. Such courses have a groomed appearance that is generally considered superior to lawns cut with rotary mowers. There is also a consequent improving effect on the health of the grass.
There have been numerous variations in the design of the basic reel mower. Many deal with the need to accurately preserve the gap between the bed knife and the revolving blades in order to maintain efficient cutting action. Rickheim, in U.S. Pat. No. 6,618,925, discloses a method of constructing a bed knife assembly that restricts the movement of the bed knife blade relative to a clamp plate. Bokon, in U.S. Pat. No. 4,563,867, shows a rotary cutter that consists of concentric circular cutting discs rather than a reel-type bale. Chandler, in U.S. Pat. No. 4,345,419, discloses a self adjusting, floating reel blade mower, as does Beusink et al. in U.S. Pat. No. 3,863,429. Crotty, in U.S. Pat. No. 2,790,293, discloses a cutting mechanism consisting of rotating flanged discs in cooperation with a toothed stationary cutter bar.
Compared to the single freely rotating solid steel blade of the rotary mower, the cutting device of the reel mower is complex and expensive to produce. It is not uncommon for a powered reel mower of the sort used by golf courses to cost several thousand dollars. The need to preserve a precise gap between the reel and the bed knife is a disadvantage of the reel type mower relative to the rotary mower, since it generally requires that the mechanism be constructed of heavy-gauge, rigid materials that are capable of maintaining proper alignment throughout long-term use.
Designs have been disclosed for revolving blade cutters without an associated bed knife. Postlewait et al. in U.S. Pat. No. 3,068,632 shows a design that consists of two long thin blades affixed to the sides of a spinning horizontal roller. Another design, disclosed by Newton et al. in U.S. Pat. No. 1,837,725, shows two resilient metal blades connected to an axle, and “revolved by the rotation thereof to cut grass, the cutting being accomplished entirely by the revolving blades.” The drawback inherent in both of these ‘bed knife-free’ designs is the same as found in the rotary mower; namely, the relative inefficiency of cutting low mass materials such as shafts of grass with purely inertial forces.
Abbrecht, in U.S. Pat. No. 2,449,042, discloses a mechanism that substitutes elongated brushes for the helical blades in the reel. The brushes provide a compliant means of sweeping the grass against the bed knife, and Abbrecht claimed more efficient, as well as quieter operation for this mechanism relative to a steel-bladed reel. The results of any attempts to reduce this design to practice are unknown.
In addition to complexity and cost, reel-type mower mechanisms suffer from another important disadvantage compared to rotary power mowers. The reel/bed knife mechanism is incapable, by itself, of mulching grass. The bed knife is set at a fixed distance to the ground and the reel sweeps each blade of grass against the bed knife only once as the mower passes. Unless a lawn is cut very frequently, any mowing system that does not mulch the cut grass generally requires that the clippings be removed for aesthetic reasons. This creates an additional task for the operator (either raking the lawn or emptying a clippings catcher), and more importantly for the health of the grass, deprives the lawn of valuable nutrients. It also creates a burden for the local municipality if the clippings are hauled away to a landfill. The practice of disposing of grass clippings, rather than mulching them, is therefore counterproductive in a compound way.
Various means have been devised for reel mowers to redirect cut pieces of grass back into the zone of the bed knife in order to be re-cut. Smith, in U.S. Pat. No. 5,400,576, discloses a mulching device for powered reel-type lawn mowers. Aske, in U.S. Pat. No. 2,599,883, discloses a clipping guide for push mowers that is meant to accomplish this task, as do Williams in U.S. Pat. No. 2,685,775, and Elliott and Johnston in U.S. Pat. No. 2,517,184. All four of these disclosures describe a cover or cowling of some sort that is intended to passively channel clippings back to the cutting zone. Perhaps because the mechanisms are passive, there is a tendency for them to become clogged, and for the re-cutting process to be haphazard.
Force, in U.S. Pat. No. 2,759,321, discloses a combined mower and mulch machine with multiple swinging blades arranged along a horizontal shaft in a manner that is superficially similar to a reel mower. The grass is cut purely by inertial forces, however, and this design suffers the same disadvantages as a powered rotary mower.
No current lawn cutting device based on the design of a reel mower is known to exist that sufficiently addresses the problem of the complexity and cost required to maintain an accurate gap between the reel and the bed knife, nor does any known design embody an intrinsic and efficient mulching function.
A few other basic cutting mechanisms have been applied to lawn mowing. One of the more successful designs entails the use of a reciprocating toothed blade in cooperation with a fixed toothed bar, in a manner similar to a hedge trimmer. Wood, in U.S. Pat. No. 468,075, discloses such a device designed to be manually operated. The Allen Scythe, produced in England from the 1930s, used a similar mechanism powered by a gasoline engine. Updated versions of the basic design are available in various models of the AL-KO Scythe Bar Mower, but their popularity seems to be largely limited to the UK, Australia, and New Zealand. This may be because the machines tend to create significant vibrations and are considered somewhat unwieldy. The exposed cutting zone at the front of the machine also represents a safety concern. These designs are also devoid of an effective mulching function.
Implements with rotating or revolving blades have been designed and used for cutting forms of vegetation much larger than grass. Rostoucher et al., in U.S. Pat. No. 6,543,210 discloses a cutting mechanism consisting of a rotor equipped with knives in recessed pockets that can be hitched to a tractor. O'Hagan, in U.S. Pat. No. 6,321,518, discloses a tubular rotor containing a plurality of swinging blades. Flail mechanisms such as these can be very effective in clearing ground of shrubs and small trees, but tend to be overkill when the task consists of removing undergrowth, rank grasses, and weeds.
Campion, in U.S. Pat. No. 1,992,119, discloses a cutting device for a lawn mower that is comprised of a pair of counter-revolving cutters that interact so that the cutting action takes place regardless of whether the mower is moved forwards or rearwards. The axes of the paired cutters, which take the form of close-tolerance nested reels, are eccentric, and the revolving cutters are active “only at the cutting plane and effective for a shearing action.” As a consequence, this is not a design that embodies a mulching function.
In U.S. Pat. No. 2,777,274, Beaumont describes a mower mechanism in which a shearing bar is positioned inside a revolving cutter drum. The shearing bar is mounted “in a substantially fixed position and does not rotate with the drum” and is “mated to the inner surface of the cylindrical drum and held substantially at the height to which the vegetation is to be trimmed so that rotation of the drum forces the grass or other vegetation against the shearing bar, whereby it is trimmed off.” Because the shear bar in Beaumont's design is mounted in a fixed position at the cutting height, the device is incapable of providing a mulching function.
Edwards, in U.S. Pat. No. 2,309,635, discloses a hybrid grass-cutting, hedge-trimming device which consists of concentric nested counter-rotating helical cutters which in theory is capable of performing a mulching function. In order to perform this function, however, the relative positions of the rigid cutting elements must be maintained within very precise tolerances in relation to each other. Since the cutting elements are concentric, the cutting action takes place around the entire circumference of the cutting head. In as much as 360° cutting is not a requirement for cutting grass, the rigidity and tight tolerances required of such a system, as well as the energy requirement to overcome friction between the cutting blades around the entire circumference, are drawbacks in the context of a device devoted to cutting grass.
The prior art fails to provide a vegetation cutting mechanism that combines the efficiency of metal-blade shearing action with an inherent mulching function in a device of relatively low mechanical complexity, light weight, and optimized energy efficiency.